Well that is actually going to be a problem with almost any infrastructure once you separate the hardware manufacturers from the OS developers.

The better comparison is Android. Where "theoretically" you can write an android app on any Android.. and just deploy it across the market and everyone with Android can now use it right?

Not quite. Anyone that uses Android will know when looking through the Market comments they get people *all the time* reporting "Force Closes Device X", "Won't launch on Device Y", "Keyboard doesn't work on Device Z".. etc. Because even an Android app that is portable still has to adhere to the hardware capabilities (and the different OS versions and manufacturer customized tweaks) across platforms.

Switching this to QT and your first sentence:
That's not entirely true. For the most part... you can take any QT app and pretty much just compile it for whatever you want. The problem comes in to will it work? Take for example the N900. There was a few Mail programs written in QT that people have ported over, and I myself recompiled one for the N900. It compiled fine, launched on the N900 fine. The problem was the UI was not optimized for a tiny screen, and all the options menu's and stuff go off the screen. Making it unusable.

But, the app itself "worked", and was cross-platform compatible, but because the original developer had no intention of a Mobile device using their product - they did not code it to be usable on them.

Apple maintains both their hardware and their software. So they can ensure that every app written for a specific OS version will work the same on their hardware because all of their hardware is very similar in performance. They don't have to play a mix and matching game of some hardware vs others.

So anyway, the point is, the disadvantage here is the same as the advantage here: Multiple peoples hands in the Pot. MeeGo (should be) no different than Android in this case.